The present invention relates to a polyester/polyamide blend composition having a low acetaldehyde content and improved properties. More particularly, the present invention relates to a polyester/polyamide blend which includes an optical brightener having a low acetaldehyde content with improved flavor barrier and color properties. The compositional blend of the invention is particularly useful for the packaging of food and beverages.
It is well known that dicarboxylic acids and dicarboxylic esters can be reacted with glycols to prepare polyesters. Polyesters are used in the fabrication of various articles for household, commercial or industrial use. Such uses include appliance parts, food and beverage containers, and auto parts. A major drawback of many polyesters is their inherent bluish fluorescence. This phenomenon is especially of concern in packaging of products wherein their appearance is as close to their natural state as desired. For example, in the packaging of foods and beverages are where the food or beverages inside a poly(ethylene-2,6-naphthalene dicarboxylate), (PEN) or polyethylene terephthalate (PET) container may appear unnatural.
Polyethylene terephatalate is widely used for the production of light weight plastic articles since PET has excellent mechanical properties such as formability and creep resistance. However, during molding or extrusion processes, acetaldehyde is formed due to degradation reaction. When the polyester is formed into an article, the acetaldehyde in the article walls migrates into the area occupied by the contents of the article. It is known that even small amounts of acetaldehyde adversely affect the flavor of foods, beverages, and the like. For these reasons it is desirable to reduce the production of the acetaldehyde during melt processing or to minimize the migration of the acetaldehyde into the package contents.
In the area of beverage containers, transparent plastic beverage containers are important to mineral water bottlers who want to convey to their consumers that the water is pure, natural and clear of contaminants. Uncolored polyesters, and blue or green colored transparent polyesters are widely used in the water packaging market. Some bottlers prefer uncolored polyester containers while others prefer colored, transparent polyesters. A slight bluish fluorescence is not objectionable for water packaging since the appearance of the water is not sufficiently altered to make the ingredients appear unnatural. The blue and green colors are natural non-objectionable colors that one sees in bodies of water (springs, streams, lakes, oceans) because of reflection of light in varying intensities from the sky or adjacent greenery. Yellow is not one of the colors used in the trade for packaging water as it does not convey purity or naturalness as does green or blue. Additionally, for some juices and carbonated beverages a bluish fluorescence in the packaging material is objectionable since it alters the natural color of the juice or carbonated beverage.
Also important to the trade is a polyester container that does not alter the taste or the chemical nature of water with acetaldehyde. Polyester resins are manufactured and processed in ways to minimize the production of acetaldehyde in the container and contents.
U.S. Pat. No. 5,340,884 discloses reducing the concentration of acetaldehyde contained a polyester by blending 0.05 weight percent to 2.0 weight percent of a low molecular weight polyamide with the polyester. The resultant polyester has an improved flavor retaining property when used for food and beverage packaging. Unfortunately, an undesirable yellow color is also imparted to the polyester. The yellowness in the resultant packaging material must be masked by the addition of a blue dye or ultraviolet absorbers. Use of compounds other than blue dyes and ultraviolet absorbers to mask the imparted yellow color is not disclosed.
U.S. Pat. No. 3,322,680 discloses using a fluorescent brightening agent or an optical brightener at an amount exceeding 50 parts per million (ppm) to improve the whiteness index of TiO.sub.2, pigmented polyester. Fibers, films, and shaped articles which have an inherently yellow color before dyeing have a decreased brightness after dyeing. The brightness of these articles can be increased by adding at least one fluorescent 4, 4'-bis(benzoazol-2-yl) stilbene compound in the amount of 0.005 weight percent (50 ppm) to 0.5 weight percent (5000 ppm). One of these compounds, (2,2'-(1,2-Ethenediyldi-4,1-phenylene)bisbenzoxazole), is sold by Eastman Chemical Company under the trade name Eastobrite OB-1.
U.S. Pat. No. 5,393,862 discloses a naphthalenedicarboxylic acid containing polymer composition with reduced fluorescence. A copolymerizable aromatic ketone having at least one acyl group directly attached to the aromatic ring is used as a fluorescence quenching agent. Fluorescence reduction in PET is not disclosed.
Accordingly, there is a need for a transparent polyester packaging material that does not have a yellow appearance and does not alter the pure natural taste or chemical nature of the water.